Effective Switchgear Protection

Vaasa Electronics (Finland) introduced the VAMP high-speed protective relay, which is designed specifically to protect switchgear against the dangers of arcing. It offers arc protection in addition to standard over-current and earth-fault protection for switchgear. With VAMP every outgoing feeder and busbars can be selectively protected against arcing short-circuits in the outgoing cable compartment.

Overcurrent and light intensity are the criteria used for arc protection. The extremely fast trip function - within 15 milliseconds - limits the damage to a minimum. Selective tripping of individual feeders also reduces the number of consumers affected by the fault that caused arcing to occur. The over-current caused by an arc is lower than the over-current caused by “metallic” short circuit; it may be lower than the over-currents caused by starting large motors. This means that the instantaneous trip stage of a standard over-current relay does not operate in the event of arcing. The trip time of the over-current stage will therefore be too long for protection against arcing. Thus a protection system based solely on over-current detection cannot protect equipment or personnel during an arcing fault.

The degree of damage caused by arcing depends principally on the duration of the arc. If an arc lasts only 0,1 sec, the switchgear needs to be checked and the insulation resistance measured before power can be re-established. With a 0,2 sec arc, the power supply will be interrupted; the switchgear must be checked; power is re-established only after minor repairs. In the event of a 0,5 sec arc the supply is interrupted, metal parts of the switchgear are destroyed and poisonous gases are emitted. An arc lasting one second destroys most of the switchgear and may cause a fire, injury to personnel and damage to property.

Vaasa Electronics’ VAMP is a new type of protection relay designed to deal specifically with the problem of arcing short circuits. Two different physical conditions a pre-set level of light intensity and over-current must be exceeded simultaneously before the relay is activated and the breakers tripped. Once exceeded, the VAMP arc protection relays reacts extremely fast - it response time is less than 7 milliseconds. Vaasa Electronics claim that no VAMP has ever made a false trip.